Q) In Simulated Draft, What Does The Win % Column Heading Mean?

A) Everything The Machine does is based on maximizing your probability to win. So Win % is your probability to win or the impact to probability to win that a certain player will have.

In the simulated draft, the Win % column means the probability that team will have to win after making that pick. At each point in the draft, as each team makes a pick, their probability to win goes up and everyone else's goes down (unless they make a bad pick - then their probability to win can go down).